The present invention relates generally to a flow rate measuring device for detecting a flow rate of a fluid. More particularly, the invention relates to a thermal type flow rate measuring device which defines an auxiliary passage within a main passage flowing a fluid and measuring a flow rate of the fluid flowing through the auxiliary passage.
As prior art of a thermal type flow rate measuring device, there is a thermal type flow meter disclosed in Japanese Patent Application Laid-Open No. Heisei 9(1997)-304140. The disclosed thermal type flow meter is formed with an L-shaped auxiliary passage in a flow passage, and a sensor element for detecting flow rate is arranged within the auxiliary passage.
On the other hand, an air flow meter disclosed in Japanese Patent Application Laid-Open No. Heisei 9(1997)-287991 includes a reversed U-shaped auxiliary passage formed within an air passage. A sensor element for detecting flow rate is arranged in the vicinity of the outlet portion of the auxiliary passage.
In case of the air flow rate measuring device for measuring an intake air of an automotive vehicle, while traveling behind a vehicle splashing a large amount of water under rainy condition, while traveling in heavy rain, rain water may easily pass through an air cleaner to penetrate into an air intake passage in a form of fine mist.
It has been known to artisan in the art that the thermal type air flow rate measuring device inherently cause output error as adhering water droplet on the flow rate detecting sensor element and keeps output error until the adhered water droplet is evaporated completely. When error is output in out put of the air flow rate detecting sensor for automotive vehicle, it becomes difficult to obtain appropriate air/fuel ratio to cause difficulty in maintaining normal engine revolution.
In case of the technology disclosed in the foregoing Japanese Patent Application Laid-Open No. Heisei 9-304140, when moisture penetrates into the air intake passage, it may directly collide on the flow rate detecting sensor element to adhere thereon to cause difficulty in obtaining accurate output.
On the other hand, in case of the technology disclosed in Japanese Patent Application Laid-Open No. Heisei 9-287991, since the flow rate detecting sensor element is disposed in the reversed U-shaped passage. Therefore, possibility that the water droplet directly contact with the flow rate detecting sensor element to adhere thereon, is quite low.
However, even with the U-shaped auxiliary passage structure, it is not possible to completely avoid adhesion of water droplet on the sensor element. Namely, when moisture penetrates into the auxiliary passage, a part of mixture may adhere on the peripheral wall of the auxiliary passage initially in a form of small water droplet. Then, small water droplets are coupled to form large water droplet.
Since large water droplet may be easily brown by air flow, the water droplet thus blown may adhere on the sensor element.
Therefore, it is an object of the present invention to provide a thermal type flow rate measuring device which can certainly prevent adhesion of water droplet onto a sensor element and thus achieve high reliability.
According to the first aspect of the present invention, a thermal type flow rate measuring device comprises:
an auxiliary passage defined within a main passage for introducing a part of fluid flowing through the main passage;
a sensor disposed within the auxiliary passage for detecting flow rate of the fluid; and
capturing means formed on an inner periphery of the auxiliary passage for capturing liquid contained in the fluid and transferring the captured liquid.
In the preferred construction, a thermal type flow rate measuring device further comprises discharging means for discharging the liquid captured by the capturing means out of the auxiliary passage.
The capturing means or the capturing means and the discharge means may be formed with one of a plurality of grooves, a plurality of beam-like ridges and a combination of a plurality of grooves and a plurality of beam-like ridges, the captured liquid may be transferred along the one of a plurality of grooves, a plurality of beam-like ridges and a combination of a plurality of grooves and a plurality of beam-like ridges,
A plurality of grooves, a plurality of beam-like ridges and a combination of a plurality of grooves and a plurality of beam-like ridges may extend from upstream side to downstream side in the auxiliary passage in a manner directed from portions on the inner periphery of the auxiliary passage where liquid passing through the auxiliary passage is hardly concentrated to portions on the inner periphery of the auxiliary passage where liquid passing through the auxiliary passage is easily concentrated.
In the alternative, a plurality of grooves, a plurality of beam-like ridges and a combination of a plurality of grooves and a plurality of beam-like ridges extends from upstream side to downstream side in the auxiliary passage in a manner directed from portions of the inner periphery of the auxiliary passage where centrifugal to be applied may be small to portions of the inner periphery of the auxiliary passage where centrifugal force to be applied is large.
A plurality of grooves, a plurality of beam-like ridges and a combination of a plurality of grooves and a plurality of beam-like ridges may extend oblique relative to flow direction of the fluid.
The capturing means and/or the discharge means may have hydrophilic film formed on the inner periphery of the auxiliary passage so that when the liquid adheres on the inner periphery of the auxiliary passage, a contact angle is less than or equal to 30xc2x0.
The capturing means and the discharge means may be a plurality of grooves, a plurality of beam-like ridges and a combination of a plurality of grooves and a plurality of beam-like ridges, and another groove coupled with a plurality of grooves, a plurality of beam-like ridges and a combination of a plurality of grooves and a plurality of beam-like ridges, extends from a portion of the inner periphery of the auxiliary passage in the vicinity of an inlet portion of the auxiliary passage and a portion of the inner periphery of the auxiliary passage in the vicinity of an outlet portion of the auxiliary passage,
The capturing means may be a plurality of grooves formed on the inner periphery of the auxiliary passage, and the inner periphery of the auxiliary passage of the portions other than those formed the plurality of grooves are provided water repellent characteristics so that when the liquid adheres on the inner periphery of the auxiliary passage, its contact angle thereof becomes greater than or equal to about 90xc2x0.
The capturing means may be a plurality of grooves formed in the inner periphery of the auxiliary passage, and the discharge means is through holes formed on at downstream side of the plurality of grooves in communication with the grooves.
According to the second aspect of the present invention, a thermal type flow rate measuring device comprises:
a sensor provided within a main passage through which a fluid flows, for measuring flow rate of the fluid in the main passage;
the main passage being curved in the vicinity of an upstream side of the sensor; and
capturing means formed on an inner periphery of the main passage for capturing a liquid carried by the fluid.
According to the third aspect of the invention, a thermal type flow rate measuring device in a vehicle control system including a thermal type flow rate control device, a control unit for controlling a vehicle on the basis of the condition of vehicle detected by the thermal type flow rate measuring sensor, the thermal type flow rate measuring device including an auxiliary passage introducing a part of fluid flowing through a main passage, and a sensor for detecting flow rate of the fluid, for detecting flow rate of the liquid,
a liquid capturing means and/or discharging means being provided on an inner periphery of the auxiliary passage.
As set forth above, the grooves and/or the beam-like ridge captures the liquid, such as water droplet to prevent confluence of liquid for growth to increase size of the water droplet and whereby to prevent splashing as blown by flow of the fluid.
Also, with suppressing occurrence of splashing of the liquid, the penetrating liquid can be efficiently discharged out of auxiliary passage. Thus adhering of liquid on the flow rate detecting sensor can be successfully prevented.
A plurality of grooves and/or beam-like ridges are formed on the inner periphery of the auxiliary passage, and, the grooves and/or beam-like ridges are coupled with another groove which extends from the portion in the vicinity of the inlet portion and continuously to be discharged out of the auxiliary passage. By this, adhering of the liquid on the mass production sensor can be prevented.
A plurality of grooves are formed in the inner periphery and the inner peripheral surface of the auxiliary passage other than the portion of the grooves is formed with a water repellent film for capturing in the grooves before growth of liquid through binding. Thus, the liquid adhering on the inner periphery of the auxiliary passage can be transferred easily so that they may be captured before growth of water droplet.
By this, splashing of the liquid can be prevented to avoid adhesion of the water droplet on the flow rate detecting sensor.
The grooves are formed in the peripheral wall of the auxiliary passage, and through openings are formed in lower side of the grooves for discharging captured liquid through the through holes. By this, splashing of liquid can be prevented and also retention of the liquid in the auxiliary passage is prevented.
The main passage is curved at upstream side in the vicinity of the portion where the auxiliary passage is mounted, and on the inner periphery of the curved main passage, the liquid capturing means is formed. For example, on the inner periphery of the curved or bent portion, a plurality of grooves or beam-like ridges are formed to prevent the liquid from splashing of the liquid.
By this, splashing of liquid can be prevented, amount of liquid to penetrate into the auxiliary passage can be reduced to lower probability of adhesion of liquid on the flow rate detecting sensor can be reduced.
With the construction set forth above, liquid may not adhere on the flow rate detecting sensor to permit stable output to realize highly reliable flow meter.
On the other hand, even when contaminant of liquid containing oil droplet, such as engine oil contained in blow-by gas, adhesion of the liquid can be successfully prevented and whereby to prevent variation of characteristics of the sensor due to clear measurement. Also, variation of characteristics of the scanning element is not splashed to prevent penetration can be prevented to whereby prevent contamination by oil to cause variation of oil.